The Złoty Stok-Trzebieszowice regional shear zone: the boundary of terranes in the Góry Złote Mts. (Sudetes)

Geological Quatterly, Vol. 40, No. 1,1996. p. 89-118

Zbigniew CYMmZMAN

The noty Stok-Trzebieszowice regional shear zone:

the boundary of terranes in the G6ry note Mts. (Sudetes)

The paper presents the results of structural md kinematic analysis of northern part of the G6ry n o t e Mts. (Sudete.~, SW Poland), where the Zloty Stok-Skrzynka tectonic zone is lrnown to occur; at present, the zone has been redefined as the a o t y Stok-Trzebieszowice shear zone. In general, the zone has M Wattitude and runs from the Tnebieszowice environs to the a o t y Stok region in a form of a belt up to 4 km wide. Domination of simple (rotational) shear mechanisms under ductile (plastic-crystalline) conditions was proven to take place here; it should be noticed that stages of dynamic recovery and dynamic recrystallization were variable. Ductile sinistral displacements within this wne caused displacement of overlying rock packages towards SSW, the displacement took place under the conditions of sinistral transpression which is similar to the situation of sinistral shear zone at Niemcza, located further northwards. Development of the zone under discussion is considered to be closely connected with an oblique collision of two terranes: the Moldanubicum one including the Snieinik metamorphic complex and the Central Sudetian one including the zone under consideration which makes up its most peripheral southwestern part. It was the Variscan orogeny (Upper Devonian-Lower Carboniferous) during which the collision happened and caused a sinistral transpression in this p a t of the Sudetes.

INTRODUCTION

A tectonic zone i n the northern part of the G6ry Zlote Mts. has been known for scores of years; the zone is most often called the Zloty StokSkrzynka tectonic zone (L. Finckh et al., 1942; J. Don, 196q S. Cwojdzifiski, 1975,1976a, 1977,1979, 1984; K. Smulikowski, 1979; M. Dumicz, 1979, 1989; J. h b a , 2. Bedkowski, 1995; among others); sometimes it is called the Skrzynka tectonic zone (I. Wojciechowska, 1993; I. Wojciechowska, P. Gunia, 1993) or Zloty Stok-Skrzynka fault zone (A. Muszer, 1989). Lately it was defined as the Zloty Stok-Trzebieszowice shear zone (Z. Cymerman, 1992a, 1995; 2. Cymennan, M. P.

Piasecki, 1994). The Iatter was selected to make the tittle of this paper as processes of regional ductile shear in the area extending from Zloty Stok to environs of Trzebieszowice

90 Zbigniew Cymerman

Fig. 1. Location sketchoithe Woty Stok-Tnetieszowimshear zone against the background of main tectonic units of the eastern part of the Sudetes (after Z. Cymeman. M. P. h k i , 1994; modified)

1 -Central Su&tian Terrane; 2 -Wry Sowie Mts. Unit; 3 -fragments of tectonically dismembered ophiolib sequence; 4- Kiodzko Unit; 5 -sedimentary mcks of the Bardo sttuctm; 6- Moldanubian Termne; 7 - ^G6ry

Orliclde ~ t s . S n i e h i k Dome; 8 - Kepmik Dome; 9 -Barradian Terrane; 10

-

^Late Variscan gmitoicls; 11 -selected boundary zone of ductile shearing; 12

-

zones of ductile thmsting;I3 - main faults; 14 - state boundary; BO - Braszowice ophiolite; RS - Bardo structure; GKZS - ~ l o d z k o - ~ i & y Stok granitoids; KM - Klodtko metamorphic complex; MSF - MarainaJ Sudetic Fault: MSFZ - Mid-Sudetic Fault Zone:

.

NBPZ ^{- -} -

North-Bohemian fault zone; NRO - Nowa ~ G d a ophiolite; N S ~ - Niemcza shear zone; RL

-

Ramzova line;

SGM

-

G6ry Sowie Mts. metamorphic complex; SM - Snieinik metamorphic complex; ZSSSZ - ^Zfoty

Stok-Trzebiesmwice shear _zone

The Zloty Stok-Tnebieszowice regional shear zone... 91

have been recognized not so long ago. This regional tectonic zone has, in generd, NEcSW trend and runs from the Zloty Stok area to the region of Trzebieszowice as a belt up to 4 km wide (Fig. 1).

The zone was given a special importance in evolution of the Sudetes. E. Bederke (1929) was of the opinion that its origin should be connected with development of the Ramzowa Overthrust, Variscan in age, which separates so called Moldanubicum from Moravicum.

Other workers included the zone into one tectonic line with the Niemcza Zone (H. Closs, 1922; L. Finckh et al., 1942). Many investigators considered this tectonic unit as the derivative element with respect to a folded structure of the northern branch of the Snieinik metamorphic complex. Analysing the so called Zloty Stok branch of the ~nieinikmetamor- phic complex, J. Don (1964) distinguished gneissic Skrzynka aniticlinorium and schista- ceous synclinorium of Orlowiec. Despite similarity in morphology and sequence of deformation, M. Dumicz (1989) distinguished two independent development sub-stages of the tectogene, the first one attributed to the snieznik metamorphic complex and the second one to the Zjoty Stok-Trzebieszowice tectonic zone.

In the last years, the Zioty Stok-Trzebieszowice shear zone was interpreted as the boundary of the Moldanubian and Central Sudetian Terranes (2. Cymerman, 1991b; Z.

Cymeman, M. P. Piasecki, 1994). In such models the Snieznik metamorphic complex was included in the Moldanubian Terrane while the Zioty Stok-Trzebieszowice shear zone in marginal part of the Central Sudetian Terrane which is characterized by (among others) abundant tectonically dismembered fragments of ophiolitic sequence (Fig. 1). Recently, M.

S. Oczlon (1993) included the entire G6ry Orlickie ~ t s . 4 n i e i n i k Dome in the so called Ligerian Terrane situated northwards of the assumed Ligerian Ocean.

Despite recognition (since couple of years) of significant role of intensive ductile deformations of shear type in tectonic evolution of the G6ry Orlickie ~ts.&ietnik. ~ o m e (2. Cymerman, 1990, 1991a, c, 1992a), a lot of questions still remains open on the tectonometamorphic development of this dome and adjacent units. This deals, among other questions, with the role and importance of faults rocks occurring in the Zloty Stok-Trzebie- szowice shear zone. Considering shear sense indicators, among others (C. Simpson, S.

Schmid, 1983; J. P. Platt, 1984; C. W. Passchier, C. Simpson, 1986; S. Hanrner, 1986; 2.

Cymerman, 19896; S. Hanmer, C. Passchier, 1991) and direction of tectonic transport (A.

Escher, J. Watterson, 1974; H. G. Ave Lallemant, 1983; J. P. Burg st al., 1987; Z.

Cymerman, 1989a, 1992b), the author has made a structural and kinematic analysis of shear zones appearing in the northern part of the G6ry Zlote Mts. The analysis throws a new light

Szkicloknlimyjny strcfybcinania~otegoStobTnebieszowicna tle~6wnychjedn(~~tektektonicmychwschod- niej c q i c i Sudet6w (wediug Z. Cymemuma, M. P. Piaseckiego, 1994; zmienione)

1 -term 6mdkowosudecki; 2-jednostkasowiog6rska; 3

-

fragmenty tyzczionkowanej tektonicmiesekwencji ofiolitowej; 4- jednostkn kiodzka; 5

-

skaly osadowe struktury bardzkiej; 6 -terra moldanubski; 7 - kopuh orlicko-hiedcka; 8 - koputa Kepmika; 9 - t e r n Barmndianu; 10 - granitoidy pdfnowaryscyjskie; 11 -

wybrane, graniczne sttefy dcinati podatnych; 12 - strefy podamych nasuniq5; 13-gl6wne uskoki; 14 -granica pattstwa; BO - ofiolit Braszowic; BS

-

struktura bardzka; GKZS - granitoidy Idodzko-dotostockie; KM -

metamoak Uodzki: MSF - sudecki uskok brzezny; MSFZ - frodkowosudecka strefa uskokowa; NBFZ -

pdmocnoczeska strefa uskokowa; NRO

-

ofiolit Nowej Rudy; NSZ - strefa Scinania Niemczy; RL

-

^linia

ramzowska; SGM

-

metarnorfik G6r Sowich; SM

-

metamorfik Snieinika; ZSSSZ

-

strefa 6cicinania Ztotego Stoku-Trzebieszowic

92 Zbigniew Cymerman

on a question of Variscan tectonic evolution in this part of the Sudetes. In addition, the analysis creats new possibilities (wider than before). for reconstruction of geometry of regional tectonic structures. Also, based on the modem structural-kinematic study the new circumstances appear for expIoration for mineralization in the G6ry note Mts., including exploration for gold among other minerals (M. Piasecki, 2. Cyrnennan, 1994; S. Speczik, 1994; A. Muszer, 1995). Therefore, the present paper is essentially aimed at presenting new structural and kinematic data dealing with the Zloty Stok-Trzebieszowice shear zone, and based on these tectonic data -presenting an evolution model of this part of the Sudetes during the Variscan orogeny.

RESEARCH HISTORY

L. Finckh et al. (1942) were the first to map the G6ry note Mts. zone before the World War 11; after the war the zone was mapped by J. Don (1964), I. Wojciechowska (1975), but above all by S. Cwojdzidski (1976b, 1979) who is the author of the first detailed geological map on the scale 1:25 000, sheets Zloty St& (19766) and Tnebieszowice (1979).

Petrographic studies of the area were carried out by (among others): J. Burchart (1960), M. Kozlowska-Koch (1973), K. Smuliiowski (1979), I. Wojciechowska, P. Gunia (1993);

mineralogic studies were conducted by S. Speczik (1994) and A. Muszer (1995). It was J.

Burchart's suggestion (1960) that intensive mylonitization of strongly heterogeneous complex of metamorphic rocks took place during the first evolution stage; then, a stage of plagioclase type recrystallization occurred, after which microcrystalline recrystallization followed. M. Kozlowska-Koch (1973) and K. Smulikowski (1979) were the authors who presented a scheme of composite metamorphic evolution of rocks in the zone under consideration; according to their opinion, the evolution was thought to be of three stages.

A number of studies were carried out in the G6ry Ziote Mts. area; they focussed on the tectonics and structure (J. Don, 1964; J. Don, R. Gotowda, 1980; I. Wojciechowska, 1975, 1986; S. Cwojdzidski, 1975,1977,1982; M. Dumicz, 1989; Z. Cymerman, 1991a, 1992a, 1995). That was J. Don (1964) who distinguished a gneissic antyclinmium of Skrzynka and a schistaceous syncIinorium of Oriowiec with Bzowiec fold within the areaunder disussion.

S. CwojdziAski (1977) was next to separate the Haniak structure, a folded structure of the G6ra Mikowa Mt.-Trzebofi, and a folded Kikol zone; all units mentioned here occur in the northern sector of the zone. In his explanations to the map sheet of Trzebieszowice, S.

Cwojdzidski distinguished macroscopic tectonic elements appearing in the southern sector of the zone. These include tectonic units of Kaczyniec, Eysy Garb, Bzowiec, Bidy KamieA, and Jawornik4rlowiec.

Many researchers were invohed in mesostructural analysis of the northern part of the Mry Zlote Mts. I. Wojciechowska (1975, among others) was the first to initiate a classical structural study; she separated four sequentional phases of tectonic deformations (Dl-D4).

Mylonitization was thought to develop in two stages: a weaker one after the phase

D2

and a stronger one after the phase

Dj.

Also S. Cwojdziriski (1976a, 1977, 1982) made some contribution to deformations overlapping by several stages; he suggested that common opinion on strong post-folding mylonitization be revised (J. Don, 1964; M. Kozlowska- Koch, 1973; I. Wojciechowska, 1975). Studying the Bzowiec fold, J. Don and R. Gotowaia

The aoty Stok-Tnebieszowice regional shear zone... 93

(1980) also recognized four stages of deformations (Dl-D4). M. Dumicz (1989) represented the idea that seven stages of deformation (Dl-D7) should be distinguished within the zone under consideration; however, structures of tectonic stages Dl and

D2

were thought to be destroyed by intensive cataclasis, mylonitization, and blastasis during stage

D3.

It was also thought that penetrative metamorphic lamination and mylonitic banding originated in that time. Also A. Muszer (1989) was of the opinion that four independent deformation stages (Dl-D4) could be separated in the southern sector of the mentioned zone. Recently, J. h b a and Z. B&owski (1995) distinguished seven stages of deformation (Dl-D7) within polymetamorphic units at Zloty Stok quarry.

The last years make up the period during which first studies containing analysis of kinematics of deformed metamorphic rocks are being published (2. Cymerman, 19914 b, 1992a, 1995; J. h b a , Z. B&owski, 1995). The importance of regional sinistral disloca- tions of strike-slip character in the eastern sector of the Sudetes and in the Fore-Sudetic Block has lately been emphasized by P. Aleksandrowski (1995) and S. Mazur and J.

Puziewicz (1995).

GEOLOGICAL SETTING

The Zloty Stok-Trzebieszowice shear zone can be divided into two parts (the western and the eastern ones). They differ from each other with respect to slightly different lithology of rock complexes, but above all -orientation of tectonic structures.

The

western part, with its surface area equal to about 10

h2,

is situated westwards of Trzebieszowice. A valley of the Bida hdecka river separates it from the S n i e i ~ k metamorphic complex ( s e m srricto) on the south; the Klodzk+Zloty Stok granitoids make up the northern boundary. In general, the NW-SE trend of lithologic boundaries and steep dips to

NE

are characteristic features of this western part. The trend of lithologic boundaries is consistent with orientation of regional foliation of penetrative type. In principle, the western part of the zone is built up of variety of amphibolites and gabbro-amphibolites (1.

Wojciechowska, P. Gunia, 1993), also plagioclase-microcline Haniak type gneisses, blas- tomylonitic schists of hornfels type and biotite gneisses as well (Fig. 2).

The eastern part of the Zloty Stok-Trzebieswwlce shear zone is much bigger in area (over 40 km2). Its more diversified rock assemblage is characterized by the occurrence of numerous mylonitic and cataclastic structures (L. Finckh etal., 1942; M. Kozlowska-Koch,

1973; S. Cwojdziiiski, 1975, 1977; I. Wojciechowska, 1975, 1993). This eastern part, extending from Trzebieszowice to Zloty Stok, is mainly composed of blastomytonitic schists and biotite gneisses (also known as gneissic blastomylonites), and blastomylonitic schists of biotite and biotite-quartzic types (Fig. 2). Of secondary importance in this assemblage are leptic gneisses (sometimes defined as the quartzic-feldspar blastomylo- nites), leptinites, quartzic-microcline-plagioclase schists, and blastomylonitic microcline paragneisses. Frequently, they are accompanied by mylonitic gneisses and so called Haniak type gneisses. The latter are composed of gneissic blastomylonites, leucocratic blastomy- lonitic gneisses, and rnigmatitized biotite-cordierite gneisses (the "Haniak gneisses" sensu stricto). Tectonic breccias (S. Cwojdzifiski, 1977) in the Zioty Stok-Trzebieszowice shear zone have sometimes been described as kakirites

(M.

Kozlowska-Koch, 1973). The eastern

The Zfoty Stok-Tnebieszowice regional shear zone... 95

part of the zone under consideration is characterized by relatively stable course of lithologic boundaries of

NNESSW

attitude and steep dip, mostIy towards

WNW,

sometimes towards ESE (Figs. 3.4).

The so called Radoch6w Anticlinorium (J. Don, 1964) within adjacent extended metamo~phic Snieinik complex sensu stricto, at the contact with the Zloty Stok-Trzebie- szowice shear zone, is the area of the occurrence of augen gneisses (also called the Snieznik gneisses). The fact is they are typical blastomylonitic gneisses that originated in the ductile shear zones (Z. Cymeman, 1991c, 1992a). Degree of intensity of simple (rotational) shear processes occurred to be a factor which

-

to some extent

-

governed a large structural- textural variability. The blastomylonitic gneisses surround so called Gierdt6w gneisses among which a number of variations can be distinguished with respect to their structure and texture (including those laminated, banded, migmatite, and others). In general, only locally the GieraIt.6~ gneisses are of mylonitic type (e.g. M. Dumicz, 1989).

The Jawornik granitoids are the rocks that occur in the Zloty Stok-Trzebieszowice shear zone close to its contact with the ~ n i e i n i k metamorphic complex. They _{form elongated} bodies of NNE-SSW trend and maximum thickness of around 1 km (Fig. 2). Dominant in these granitoids are monzonitic granites with weak fabric, granodiodtes, and tonalites (J.

Burchart, 1960; S. Cwojdziiiski, 1977, 1979). Parts of these granitoids were subjected to strong mylonitization; this fact indicates that mylonitization processes continued also after generation of the Jawomik granitoids (S. Cwojdzidski, 1979).

DUCTILE SHEAR ZONES

The ductile shear zones are the structural domains with characteristic accumulation of large deformations in relation to envelope rocks (protolith) and noncoaxial progressive

Fig. 2. Geologicalmapof thenoty Stok-Tnebie6zowiceshenrzone (afterS. Cwojdzihski, 1976b, 1979;simplified) 1 -Cenozoic formations; 2 -Cenozoic basaltoids; 3 -IUodzko-Ztoty Stok granitoids; 4-Jawornikgranitoids;

5 - hornfels-type blastomylonitic schists and biotite gneisses; 6 - cataclasites of Haniak gneisses; 7 -my lonitic gneisses and cataclasites; 8 - mylonitic gneisses and mylonites; 9 - plagiocle-micmclhe gneisses with cordierite (the Haniak type gneisses); 10 - plagioclasemicrocline gneisses (the G i e d 6 w type gneisses); 11

-

oligoclasemimcline augen gneisses (the gnieinik type gneisses); 12

-

micaoeous blastornylonitic schists and biotite gneisses; 13 -1eptinites and leptitic gneisses; 14- amphibolites and amphibolic schists;,l5 -crystalline limestones and calcareous-siliceous rocks; 16 - micarnous schists and plagioclase paragneisses (the Stronie Series); 17-faults; 18-geological boundaries; 19 -state b u n d a y ; 20-cmss-section A-B; USB -Marginal Sudetic Fault

Mapageologicma strefy icinaniaztotego Stoku-Trzebieszowic (wedtug S. Cwojdziliskiego, 1976b, 1979; uprosz- czona)

1 - utwory kenozoiczne; 2

-

b d t o i d y kenozoiczne; 3 - granitoidy ktodzko-ztotostockie; 4

-

granitoidy jawomickie; 5

-

zhornfelsowane tupki blastomylonityczne i gnejsy biotytowe; 6 - kataklazyty gnejsdw haniackich; 7 - gnejsy mylonityczne i kataklazyty; 8 - gnejsy myloniqczne i mylonity; 9

-

gnejsy plagiokla- zowo-mikroklinowe z kordierytem (gnejsy typu haniackiego); 10- gnejsy plagioklozowo-mikmklinowe (gnejsy typu gierdtowskiego); 11 - oczkowe gnejsy oligoklazowo-mikroklinowe (gnejsy typu biehickiego); 12 -

lyszczykowe tupki blastomylonityczne i gnejsy biotytowe; 13 - leptynity i gnejsy leptytowe; 14 - amfibolity i h p k i amtiboiowe; 15

-

wapienie krystaliczne i skaty wapienno-laemirnowe; 16 - hpki lyszczykowe i paragnejsy plagioklazowe (seria stmhska); 17 - uskold; 18 -granite geologicme; 19 - granica palistwowa; 20

- linia pnekmju A-B; USB

-

sudecki uskok brzeiny

Pig. 3. Geological-structural cross-section A-3

1 -sense of displacement towards the viewer; 2 -6ense of displacement from the viewer; for other explanations see Fig. 2

Pnekr6j geologicmo-strukturalny w d u i linii A-B ^-

1 - zwrot pnemieszczenia w strone obserwatora; 2

-

zwrot przemieszczenia od obserwatora; pozosde objd~enia jak dla fig, 2

deformation approximated to the simple shear (e.g. W. D. Means et al., 1980; G. S. Lister, P. F. Williams, 2983; T. H. Bell, R. L. Hammond, 1984; S. Hanmer, C. Passchier, 1991).

Shear zones are common on all scales, from microscopic streaks up to regional structures (e.g. T. H. Bell, 1978,1985; R. D. Law et al., 1984; A. Vauchez, 1987; A. G. Goldstein, 1989; S. Hanmer, f 990; P. R. Cobbold et al., 1991 ; R. Girard, 1993). In general, shear zones comes into being when hardening ability of rock material has been overcome and localized softening strain processes have started to develop. As concluded from rheology, ductile deformations can also appear as the resuIt of brittle mechanisms of deformations or due to combination of cataclastic and plastic deformations under lower temperature and pressure than those required for plastic penetrative deformation (e.g. R. D. Law eE al., 1984; S.

Hanmer, C. Passchier, 1991; W. D. Means, 1990;

H.

Fossen, B. Tikoff, 1993). It is common that the shear zones are considered to be intensive nonhomogeneous deformations subjected to the softening strain processes.

Traditionally, the term "mylonite" was used to define a rock with characteristic reduc- tion of pain size due to cataclastic process. As the idea is still common that mylo~tization process is always followed by reduction in grain size, insufficient effort.was exerted in recpgnizing many mylonitized fault rocks subjected to syntectonic recrystallization and increase of mineral grain size during development of ductile she* zones. This resulted in considerable simplification of terminology of so called fault rocb and their essential division into the cataclastic rocb and the mylonitic ones. Transition from frictional flow to viscous flow is the essential criterion of this genetic ~Iassification of the fault rocks.

A definition of mylonite as presented in this paper is based on the G. S. Lister and A.

W. Snoke's suggestion (1984) to consider it as a rock being formed as the result of intensive

The Zloty Stok-Trzebieszowice regional shear zone... 97

deformation that have been accumulated through cystallineplastic behaviour of matrix.

Important to note here is the fact that matrix minerals have been subjected to extended penetrative and dynamic recrystallization along with synchronic reduction of mineral grain size; they have also formed a well arranged crystallographic structure (comp:

R.

D. Law et al., 1984; T . H. Bell,

R.

L. Hammond, 1984; W. D. Means, 1990; S. Hanmer, C. Passchier, 1991). Generation of mylonite will always remain under the influence of deformation parameters and processes of softening strain. From mechanical point of view, a softening can be defined as the reduction of stresses at constant rate of deformation or as an increase of strain rate at constant regional stress. The softening strain can include a number of different processes such as, for example: change in deformation mechanism, progressive recrystallization, softening as the result of chemical reaction, warming up in effect of both shearing and fluid pressure. It should be noticed that rapid expansion of ductile shear zone can take place if a rock has not been affected by the softening strain.

FOLIATIONS

Structures of planar (foliations), linear, and folded types together with kinematic indicators were employed to analyse the Zloty Stok-Tnebieszowice shear zone from the structural and kinematic point of view; adjacent Snieznik metamorphic complex was also analysed (Fig. 4). Compilation of foliation measurements within the Zloty Stok-Trzebie- szowice shear zone is presented in two diagrams, separately for the northern part (Fig. 5A) and the southern one (Fig. 6A). Similar point diagrams have been prepared for adjacent Snieinik metamorphic complex, individually for the

NE

part (Fig. 7A) and the

NW

one (Fig. 8A). Orientation of linear and folded structures existing within the Zloty Stok-Trze- bieszowice shear zone (Figs. 5B, 6B) andadjacent Snieznik metamorphic complex has been included in the'point diagrams (Figs. 7B, 8B). Only the most representative measurements, averaged from almost 40 observation points from the Zloty Stok-Trzebieszowice shear zone and almost 50 outcrops in adjacent Snieinik metamorphic complex are included in the diagrams compilation. More abundant tectonic data, compiled in both point and contour diagrams for the area under consideration are available in the works by S. Cwojdzifiski (1976a, 6,1977, 1979), J. Don and R. Gotowala (1980), and M. Dumicz (1989).

Penetrative foliation in the Zloty Stok-Trzebieszowice shear zone was determined as

Sl

(e.g. I. Wojciechowska, 1993; J. Don, R. Gotowda, 1980; A. Muszer, 1989) or S2 (coplanar with respect to S1) (S. Cwojdzifiski, 1976a, 1979; M. Dumicz, 1989), also as S3 (I. Wojciechowska, 1975). S. Cwojdzifiski (1982, p, 176) expressed an opinion that

"...intensive shearing

...

taking place in the foliation plane was the factor governing the structural and textural development of metamorphic rocks". Micro- and mesoscopic obser- vations from the Zloty Stok-Trzebieszowice shear zone are in full agreement with that former conclusion.

It should be noted that so called penetrative (regional) foliation is a combined structure composed of two (sometimes three) sets of planes: foliation planes (S) that cumulate the final deformation, and shear planes (C), development of which is connected with discon- tinuous ductile flow. It is a structure of

S 4

type (Figs. 9-11) which is characteristic for ductile shear zones (C. Simpson, S. Schmid, 1983; G. S. Lister, A. W. Snoke, 1984; C.

The Boty Stok-Tnebieszawice regional shear zone... 99

Simpson, 1986; Z. Cymerman, 1989b; _S. Hanmer, C. Passchier, 1991). The C planes are oriented parallel to boundaries of shear zones and to dominant flow plane; usually, they are exposed as narrow zones with blastic grains and oriented arrangement of phylliosilicates.

The S planes are, in general, situated at an angle of 45" to boundaries of shear zones and they define the XZ plane of finite strain ellipsoid. With the increase of dislocation rate, the S planes rotate to reach a close parallelism to the boundary of the ductile shear zone. The S planes are usually made up of phyllosilicates and directionally elongated quartz and feldspar grains.

A localized foliation appears in rocks subjected to intensive shear dislocations; they are given the SB (Figs. 11,13) or C' designations and are defined as an extensional crenulation cleavage (J. P. Platt, 1984) or asymmetrical extensional shear bands (L. B. Harris, P. R.

Cobbold, 1985; S. Hanmer,

C.

Passchier, 1991). The SB planes are, in general, dipping at 15-25' angle towards a bulk flow plane.

It is characteristic in the Zjoty Stok-Trzebieszowice shear zone that the combined penetrative foliation is gradually changing its spatial orientation, from close to meridional in the northern part of the zone Figs. 4, 5A) to almost parallel in the southern and southwestern parts (Figs. 4,6A). In general, foliation of NNESSW orientation dominates at medium and large dip angles towards

N W

in the SW part while towards E in the NE part (Figs. 4,5A, 6A). The point diagrams of foliation (Figs. 5A, 6A) clearly indicate stronger scattering of foliation attitude with respect to the Snieinik metamorphic complex (Figs. 9, 11). This provides evidence on stronger, more heterogenetic deformation due to shearing and on subsequent, intensive folding of foliation plane in the shear zone in comparison with the Snieinik metamorphic complex.

Orientation of combined regional foliation in the Snieznik metamorphic complex in its NE part is different £rom that in the

N W

part (Figs. 4,7A, 8A). The foliation strikes in the

NE

part are arranged almost parallel to the Zloty Stok-Trzebieszowice shear zone, with dominant medium and low angles of dip towards

N W

pig. 7A). The foliation in the northwestern part of the Snieknik metamorphic complex is characterized by rather medium angles of dip, but towards

NE,

this time (Fig. 8A).

Fig. 4. Structural-kinematic map of the Uoty Stok-Tmbieszowice shear zone (after Z. Cymennan, 1991b;

supplemented)

I -strike and dip (7b90") of steep penetrative foliation; 2- sfrib and dip of penetrative foliation with dip angle in the range of 4049'; 3 -strike and dip of penetrative fdliation with dip angle in the range of LL39'; 4-strike and dip angle (0-30') of penetrative lineation; 5 -strike aad dip angle (more than 30") of penetrative lineation;

6 - senses of displacement of sfrikeslip type; 7 -senses of displacements of normal "faulting" (extensional) type; 8 - Cenozoic basaltoids; 9 - Kbdzko-Po@ Stok granitoids; 10 - Jawomik granitoids: 11

-

faults; 12 -geological boundaries; 13 -state boundary; USB -Marginal Sudetic Fault

Mapa strukturalno-kinematycma strefy gcinania Zbtego Stoku-Trzebieszowic (wediug Z. Cymennana, 1991b;

uzupeloiona)

1 - bieg i upad (70-90") stromej foliacji penetmtywnej; 2

-

bieg i upad foSiacji penetratywnej o W i e upadu 40-69"; 3 - biegi upad foliacji peneeratywnej o we upadu LL39"; 4-kierunek i kqtnachylenia(0-303 lineacji penetratywnej; 5 - kiexunek i kg nachylenia (powyiej 30') lineacji penetratywnej; 6 - zwroty ptzemieszczefi typu przesuwczego; 7 --zwrotyprzemieszcze6typu .pskokowania"normalnego (ekstensyjnego); 8

-

bazaltoidy kenozoiczne; 9

-

granitoidy klodzko-ziotostockie; 10

-

granitoidy jawornickie; 11 - uskoki; 12 - granice geologicme; 13

-

granica pdstwa; USB

-

sudecki uskok brzeiny

Fig. 5. Point type diagram of planar (A) and h e a r and fold type (B) structures for the northern part of the Zloty Stok-Tnebieszowice shear zone; lower hemisphere of the Schmidt's net

A: 1 -pale of undifferentiated, complex, penetrative foliation; 2 -pole of plane S for S-C type structm; 3 - pole of plane C for $4 type structure; 4 - asymmetric extensional shear bands of SB typt; B: 1 - lineation of mineral grain; 2 -intef~ectionaI lineation; 3 -lineation of crenulation type; 4 - boudinage; 5 -isoclinal and tight folds; 6 -tight folds; 7 -tight asymmetric folds; 8 -open folds; 9 -open asymmetric folds; 10 - fault folds; 11 - fault asymmetric folds; 12 - open bmad folds

A: 1 - biegun nierozdzielonej, zbanej foliiji penetratywnej; 2- biegun powiwzchni S ze struktury typu S C , 3 - biegun powierzchni C ze struktury typu S-C; 4

-

asymetryczne, elcstensyjne pasemka Lcinania typu SB; B:

1 - lineacja ziarna minerahego; 2 - lineacja intersekcyjna; 3 -1ineacja typu unarszczkowania; 4

-

^budinai,

5 - fddy izoklinalne i w@kopromienne; 6 - fddy w~kopromienne; 7 - fddy w$skopromienne, asyrnetryczne;

8 -fddy otwarte; 9

-

fddy otwarte, asymetryczne; 10- faidy miomowe; 11 - fddy zaiomowe, asymetryczne;

12 - fddy otwarte, szerokopromie~e

Apart of potes of undivided, combined, penetrative foliation, the following elements have for the f i s t time been plotted on the point diagrams: poles of the S and C surfaces of

S4!

type structures and poles of mylonitic asymmetric extensional shear bands of SB type for bpth the Zloty Stok-Trzebieszowice shear zone pigs. 5A, 6A) and the adjacent Snieinik metamorphic complex (Figs. 7A, 8A). The collected data documents the sinistral senses of shearing in the zone under consideration and dextral senses of,shearing within the NW part of the Snieznik metamorphic complex. There are also sinistral senses occurring in the Snieznik complex, co-existing with the dextral ones. The sinistral senses of shearing become dominant in the boundary area between the Zloty Stok-Trzebieszowice shear zone and the Snieinik metamorphic complex.

The Zloty Stok-Trzebieszowice regional shear zone... 101

Fig. 6. Point type diagram of planar (A) and linear and fold type (B) structures for the southern part of the Zloty Stok-Trzebieszowice shear zone; lower hemisphere of the Schmidt's net

For explanations see Fig. 5

Diagram punktowy stnrkCur planamych (A) oraz sttukhlr linijnych i faldowych (B) z poludniowej c d c i strefy Scinania Ztotego Stoku-Trzebieszowic; dolna p6Ikula siatki Schrnidta

Objdnienia jak na fig. 5

LINEATIONS

Such linear structure as the lineation of mineral grain occurring in the entire Zloty Stok-Trzebieszowice shear zone is the structure with features of Lx extensional lineation.

The extensional lineation, also known as extensional lineation or mylonitic lineation or lineation due to elongation, always develops on the foliation planes; its orientation during progressive deformation of plane strain type or constriction strain type is always parallel to axis X of finite strain ellipsoid (X

>

Y > Z) andlor axis X of incremental strain ellipsoid (23.

E. Hobbs etal., 1976; H. G . AveLallemant, 1983; Z. Cymeman, 1989a, 1992b). Atpresent, the extensional lineation of Lx type has found a wide application to determination of tectonic transport direction (e.g. H. Ave Lallemant, 1983; J. P. Burg et aL., 1987; Z. Cymerman, 1989a, 1992a;

N.

Urban, 1992; H. Fritz, F. Neubauer, 1993; S. Mazur, J. Puziewicz, 1995).

Most often, morphology of lineation of Lx type is pointed out by directional arrangement of mineral grains on the foliation planes that developed as the result of dynamic recrystal- lization andlor dynamic recovery. Of such type is the penetrative lineation

0)

in the Zloty Stok-Trzebieszowice shear zone and the Snieinik metamorphic complex as well. The penetrative lineation of grains and aggregates in gneisses is pointed out by directional elongation of eyes, rods, and mineral aggregates; this mostly deals with quartz and feldspars, and micaceous packages as well. The Lx lineation in micaceous schists and plagioclastic paragneisses is detkrmined by arranged elongation of micas, and rods and ribbons of quartz and plagioclases.

Fig. 7. h i n t type diagram of planar (A) and linear and fold type (B) structures for the northeastern part of the Snieinik metamolphic complex; lower hemisphere of the Schmidt's net

For explanations see Fig.5

Diagram punktowy sttuktur planamych (A) oraz strdctur linijnych i fatdowych (B) z p6hocncbwschodniej c&a metarnorfiku Sniemika, dolna pr5tkula siatki Schmidta

Obja5nienia jLna fig. 5

There is characteristic relatively stable spatial orientation of ~e Lx lineation within the Zloty Stok-Trzebieszowice shear zone; it takes a NE-SW attitude at low and medium plunge angles, mostly towards SW and S, and also to.NE (Figs. 4,5B, 6B). Some deviations from this regional direction are relatively common in the northern part of the zone; the Lx plunges here to S or SE (Figs. 4,5B). As refers to the southern part of the shear zone, the Lx lineations plunge towards W and E too (Figs. 4,6B).

In that part of the Snieinik metamorphic complex which is situated southwestwardly of the Zloty Stok-Trzebieszowice shear zone, orientation of the Lx lineation is almost the same as that in this shear zone (Fig. 7B), however, the trend of the Lx orientation is quite different in the NW part of the Snieznik metamorphic complex (the Krowiarki Range). The exten- sional.lineations we of NW-SE orientation here, at low and medium plunge angles, in genera1 towards

N W

(Fig. 8B). The area in the vicinity of Trzebieszowice where a change appears in the structural trends within the Snieinik complex, was defined as the area of the W e k virgation (J. Don, 1964). Despite some, sometimes considerable deviations from regional trends in orientation of the Lx lineation those variances seem to be rather progressive and closely connected with heteragenetic deformation in shear zones of anastornosing type andlor subsequent folding (Figs. 12.13) of penetrative foliation planes on which the Lx lineation developed.

Since the Lx lineation is almost parallel ta orientation of majority of fold axes, then the Lx lineation was commonly considered to be of type B. It mean that lineations of mineral grains (Lx) and fold axes (structures of type B) developed perpendicular to axis

al

of main stress. Close parallelism of orientation of both fold axes and lineation Lx is a very characteristic feature of strongly deformed regions of all orogenic ranges (e.g. A. Vauchez,

The aoty Stok-Mitszowicc @rial shear m... 103

Fig. 8. Point type diagram of planar (A) and linear and fold trpe @) structures for the northuestem part of the sniehikmetamorphic complex; lower hemisphere of the Schmidt's net

Fa explanations see Fig.5

Diagram punktowy struktur planarnych (A) araz struktur linijnych i fddowych (3) z p6hocno-mcbdniej c&ci metamorfilcu Snieinika, dolnap6lkulasiatlci Schmidta

Objadnienia jak na fig. 5

1987; R. E. Holdsworth, 1990; D. Cassard et at., 1993). Currently, parallelism of lineations and folds arrangement is considered to be the result of intensive defonnations due to shearing and successive rotation of fold axes in direction of shearing during progressive deformation (A. Escher, 1. Watterson, f 97% T. H. Bell, 1978; P. R. Cobbold, H. Quinquis, 1980).

The L;x lineations in the. Zloty Sbk-Trzebieszowice shear zone are oriented almost parallel tn axes of isoclinal and tight folds that traditionally have been designated as F1 and

F2

structures (e.g. I. Wojciechowska, 1975, 1986; S. CwojdziRski, 1976a, 1977, 1982; J.

Don, R. Gotowda, 1980; M. Dumicz, 1989). At the s w e time the Lx lineations are more oblique with respect to open fold's axes of significantly larger interlimb angles. These facts document well the process of progressive deformation due to shearing; apart from rotation, the process also included modification of fold shape. During this process, the large and open-type folds developed here, then

-

following the increment of deformation due to shearing, the folds became more and more tight and closed. Angulat differences between the Lx lineation of extensional type and the axes of majority of open. folds and crenulations (gouffrage) does not nec+ssmjly indicate different development of linear and folded structures. On the contrary, non-coaxiality of structures of such type could be caused by their synchronous development, but only in such circumstances in which their origin and evolution were taking place during progressive simple shearing (A. J. Dennis, D. T. Secor, 1987).

In a number of sections XZ (perpendicular to foliation plane and parallel to the Lx lineation) of the Snieinik gnei'sses, observations were made of progressive development of

fig. 9. Augen gneiss with planar stmctures of S 4 m e and porphyroclasts of type. a; vicinity of Radoch6w; scde in centimeWs

Gnejs oczkowy ze struktu~wni planarnymi typu S 4 i porfiroklastarni typu 0; okolice Radochowa; skala w centymemh

Fig. 10. Biotitegneiss showingstrongrecrystallization of planar structureof S-C type; vicinity of Woty Stok; scale in centimetres

Gnejs _biotytowy z sih+relaystalizacj$ struktury phamej m u S-C; okolice Zlotego Stoku; skala w centymetrach

The Baty Stok-Trzebieszowioe regional shear zone... 105

Fig. 11. Blastomylonitic schisk with indicators of shear serises (structures of S-C and SB types); vicinity of Shzynka; scale in centimetres

Lupki blastomylonitycme rc w s Wzwrotu Scinania (strulttury erpu _S-C i SB); okoIice Slay&, skala w centymettach

Pig. 12. Asymmetric fold type stnrctum in plagioclase paragneisses (the Stronie Series); vicinity of L&& Zdrdj;

scde in centimetres

Asymetryczne sfruktury fddowe w paragnejsach plagioklazowych (seria stmriska); okotice LBdka Zdroju; s M a w centymetrach

Fig. 13. Asymmetric quartz lense and synthetic struc- ture of asymmetric extensional shear zone; blastomy- lonitic schists; vicinity of Odowiec

Asymetrycmasoczewaharcui synietycznastruktu- ra typu asymetrycznej ekstensyjnej sttefy Gcinania;

lupki blastomylonityczne; okolice Odowca

rodding type lineation closely connected with intensification of simple shear process. With intensification of shear deformations, large K feldspar megacrystals became more and more prolate, and elongated. Process of reduction of feldspar megacrystal size contributed to gradual development of very characteristic asymmetric feldspar eyes, mostly microcline, defined as porphyroclastics of type cr (e.g. C. W. Passchier, C. Simpson, 1986; H. Takagi, M. Ito, 1988; Z. Cymerman, 19896, 1992a; S. Hanmer, C. Passchier, 1991). If a simple shear is overprinted by other simple shear or other non-coaxial strain (general shear, for example) (W. D. Means, 1990; S. Hanmer, C. Passchier, 1991), the

Lx

lineation may be oriented between axes X and Y of the finite strain ellipsoid. Such a situation is rather common in the case of non-planar deformation, when volume of rock subjected to defor- mation has been changed. It should be emphasized here that in the event of non-plane deformation it is impossible to explicitly determine a direction of tectonic transport based on orientation of the Lx extensional lineation. Such a case is rather not connected with the area under discussion, where the total deformation being mostly close to the plane defor- mation (X > Y = 1

>

Z) and direction of tectonic transport does not change in a significant way; also, there is no distinct rheological difference between constituents of Lx mineral lineation and the remaining part of the. rock.

S m A R SENSES

A kinematic-smctural analysis carried out in the plane parallel to Lx lineation and perpendicular to foliation (aXZ plane of the finite strain ellipsoid) has allowed to determine shear senses. The senses have been determined for 39 points within the Zloty Stok-Trze- bieszowice shear zone and the closest vicinity of the Snieinik metamorphic complex (Fig.

4).

Based on asymmetry of tectonic structures, different criteria were applied to determine the shear senses (e-g. C. Simpson, S. Schmid, 1983; C. Simpson, 1986; 2. Cymerman, 1989b,1991a, c, 1992~). In the case of augen gneisses, the shear senses were determined from porphyroclastics of type

cr

(Fig. 9) and 6 (C. Simpson, S. Schmid, 1983; T. H. Bell, 1985; C. W. Passchier,

C.

Simpson, 1986; J. van der Driessche, J. P. Brun, 1987; S. Hanmer, 1990) and mylo~tic structures of S-C type discussed before, in chapter dealing with foliation (Figs. 9-1 1). Shear senses in the migmatized and Haniak gneisses were mainly determined from oriented thin sections according to an oblique fabric (e.g. R. D. Law et al.?

1984; S. Hanmer, C. Passchier, 1991). The oblique fabric and so called mica fishes were

The Zloty Stok-Trzebieszowice regional shear zone... ¹⁰⁷

Fig. 14. Example of fold structures; leptinites; Bzo- wiec Mt.

Przykladdefonnacji fddowych; leptynity;g6raBzo- wiec

the best indicators in mylonitic schists and gneisses (e.g. S. Hanmer, 1986; Z. Cymerman, 1992~); in most cases they were determined from oriented thin sections. Also, relatively abundant non-penetrativesynthetic planar structures of asymmetric extensional shear bands of SB type were observed in mylonitic rocks (Figs. 11,13) (R. Weijerrnars, H. E. RondeeI, 1984; J. P. PIatt, 1984; L. B. Harris, P. R. Cobbold, 1985; S. Hanmer, C. Passchier, 1991);

asymmetric quartz rods (Fig. 13), asymmetric boudinage structures (e.g. S. Hanmer, 1986;

S. Hanmer, C. Passchier, 1991) and kink-bands folds were also observed (Fig. 15) (L. B.

Harris, P. R. Cobbold, 1985; S. Hanmer, C. Passchier, 1991).

Data acquired from analyses of shear sense indicators for the Zloty Stok-Trzebieszo- wice shear zone points out a stable sinistral sense of shear (almost 95% of kinematic data).

It documents sinistral displacement of strikeslip type on steep foliation planes along with almost horizontal extensional lineation Lx (Figs. 4,5A, 5B, 6A, 6B).

DEFORMATIONAL PARTITIONING

Most likely, synchronous and progressive development of varied fold structures (Fig.

14) and ductile shear zones within thezloty Stok-Trzebieszowice shear zone was connected with mechanism of deformational partitioning consisting in division of total deformation into domains of simple shear (non-coaxial deformation) and domains ofpure shear (coaxial deformation). In Polish literature a question of deformationaI partitioning was discussed by Z. Cymerman (1988). In the last years a number of works were published to present different aspects of deformational partitioning; regional examples were also discussed (e.g. G. S.

Lister, P. F. Williams, 1983; T. H. Bell, R. L. Harnmond, 1984; T. H. Bell, 1985; M. A.

Evans, W, M. Duhne, 1991; S. M. Cashman et al., 1992; J. Jackson, 1992; H. Fossen, B.

Tikoff, 1993; R. Girard, 1993).

In general, a simpIe shear component dominated in some part of domains as the result of deformational partitioning. The simple shear component has lead, among others, to development of S-C type structures, asymmetric porphyroclastics, asymmetric mica fishes,

Fig. 15. Asymmetric fold of kink-bands type; blasto- mylonitic schists; vicinity of Skrzynka

Asymetryczny M d zdomowy typu kink-bd;hpki bIastomylonityczne; okolice Slaynki

and extensional shear bands. A pure shear component dominated in remaining domains where folds and crenulations developed. There are intermediate domains between both extreme domains, characterized by mixed mechanism of deformation such as general shear, for example (S. Hanmer, C. Passchier, 1991).

Before now, S. CwojdziAski (1982) assumed that "...relics of older non-tectonic fold structures..

."

have been preserved in the "predisposed" domains. Most likely, these domains originated as the result of deformational partitioning; they are not the older relics but domains of pure shearing. Ebcksses of defomational partitioning are to large extent dependent on lithologic differentiation, orientation of earlier anisotropy planes, and both pressure and temperature conditions during regional metamorphism (e.g. processes of deformational softening at low rate of deformations and at high temperature).

In the G6ry Zlote Mts., the most intesive development of simple shear zones took place in rnylonitic schists (phyllonites), mylonites, and mylonitic gneisses whereas pure (rota- tional) shear component dominated in micaceous schists andmigmatite gneisses.

Almost uniform kinematic-structural picture for the Zloty Stok-Trzebieszowice shear zone indicates a stable orientation of principal strain axis. Earlier structural study of the Orlowiec area also suggested preservation of stable orientation of strain axis (J. Burchart, 1960). History of deformation, composed of stages of deformation and comprising pro- gressive increments of deformations (the incremental strain ellipsoid) up to the state of final deformation (the finite strain ellipsoid) has been defined as the progressive deformation.

PROGRESSIVE DEFORMATIONS

Jn classical structural geology an assumption was common that total deformation is of epizodic character and that consecutive stages during timely differentiated regional "epi- zodes" have caused formation of separate generation of structural elements. This concept of so called overprinting of generations of structures does not necessarily means epizodic deformations. From consideration of (for instance) two consecutive tectonic structures a conclusion can be drawn that both could originate during stages separated from each other by hundred million years or could come into being during a continuous progressive

The Zloty Stok-Trzebieszowice regional shear zone... 109

deformation (B. E. Hobbs et aL, 1976). New evidences are still appearing indicating that, in general, deformations were of continuous character and that more than one generation of structures formed during individual progressive deformations (T. H. Bell, 1978; P. R.

Cobbold, H. Quinquis, 1980; H. Helrnstaedt, J. M. Dixon, 1980; J. P. Platt, 1983; 0. T.

Tobisch, S. R. Paterson, 1988 ; R. E. Holdsworth, 1990; C. K. Mawer, P. F. Williams, 1991).

It is common that complicated relationship of overprinting (superposition) among structures may cause a false idea on independent phenomena (0. T. Tobisch, S. R. Paterson, 1988; C. K. Mawer, P. F. Williams, 1991). Processes of overprinting at the time of progressive deformation can be caused by spatial differences in the rate of deformation (J.

P. Platt, 1983; R. E. Holdsworth, 1990), kinematic enlargement of deflection on anisotropy planes (P. R. Cobbold, H. Quinquis, 1980), or changes in orientation of principal stresses with respect to earlier tectonic structures (H. Helmstaedt, J. M. Dixon, 1980). It should be remembered that usualIy it is not easy to separate an epizodic deformation from a pro- gressive one, particularly when reliable data on age of deformation is missing. In the absence of radiometric data for the Zloty Stok-Trzebieszowice shear zone, only structural-kinematic criteria can be applied; the said criteria are based on geometry of tectonic structures, shear factors, relationship between different structures, and distribution of those structures with respect to change in intensity of deformation (under the conditions of defonnational partitioning, for example) (T. H. Bell, 1978; 0. T. Tobisch, S. R. Paterson, 1988; R. E.

Holdsworth, 1990).

Manifestation of locations of stronger deformations, also those occurring within limbs of large tectonic structures such as the Bzowiec fold among others, and similar kinematic display for the entire Ztoty Stok-Trzebieszowice shear zone is consistent with a model of progressive deformation. Indirectly, it also suggests large-scale deformational partitioning to take place during deformation. An agreement between general kinematic frames during folding in the Zloty Stok-Skrzynka zone and the stability of direction of tectonic transport towards SW suggests a sequence taking place in development of tectonic structures during individual and, in principle, continuous tectonic process. And though each separate gener- ation of tectonic structures (mostly of folds) couId be caused by a separate pulse of deformation, a general similarity of kinematic frames is much easier to explain using a concept of progressive deformation than by particular deformational. epizodes.

Development by stages within the Zloty Stok-Trzebieszowice shear zone as suggested on the basis of variability of folds' geometry (Fig. 5B), their dispersion and vergence, most often from stage Dl and D4 (e.g. S . Cwojdzibski, 1975, 1976a, 1979; 1. Wojciechowska, 1975,1993; J. Don, R. Gotowala, 1980; M. Dumicz, 1979,1989) results from deformational partitioning during progressive increments of deformations within stabIe stress field rather than from the effect of superposition of structures that originated during different stages of deformations within variable stress field.

Recently, J. h b a and Z. Bdkowski (1995) presented a sequence of up to seven consecutive generations of shear zones (S1S7) in the vicinity of Zloty Stok. During undifferentiated stages

Dl

and

D2

of deformations, the oldest foliation known under the term SI+S2 was expected to originate. This foliation was described as the mylonitic structure, and sense of tectonic displacements on those penetrative planes - as a reversed one (as concluded from figures contained in their paper), or top-to-the W oriented. However, important to note heie is the fact that those senses have been defined on improper planes

1t0 Zbigniew Cymerman

(i.e. planes perpendicular to foliation and also to lineation, thus on the

YZ

planes of the finite strain ellipsoid). The shear senses should always be determined on the XZ plane of the finite strain ellipsoid (e.g. Z. Cymennan, 19898; S. Hanmer, C. Passchier, 1991);

therefore, the J. h b a and 2. B&owski's (1995) concept of kinematic stage Dl-D2 cannot be considered correct. Moreover, the most brittle fault of both authors consists in their interpretation of extreme lineation Lx as "...the commonly observed mylonitic lineation

..."

(p. 23) which should be considered the lineation

L3.

Development of mylonitic foliation and mylonitic (extensional) lineation Lx is always synchronous and forms a matrix of mylonitic rock. Penetrative extensional lineation (by both authors improperly designated

&)

had to form synchronously also on penetrative planes of mylonitic foliation which by bolh authors was considered to be the S1+S2 structure. Therefore, the penetrative foliation and the lineation under discussion are the synchronous structures that have been formed during the main deformation.

RELATIONSHCP BETWEEN FOLDS AND SHEAR ZONES

Classical reconstructions of kinematics of deformation stages in the Sudetes (including the Bate G6ry Mts.) were based on assessment of fold vergence (Figs. 12, 14). However, axes of different folded structures can develop perpendicularly, obliquely, and parallelly to axis X of the finite strain ellipsoid (e.g. J. Ridley, 1986; J. P. Burg et aL, 1987; S. Hanmer, C. Passchier, 1991; J. Jackson, 1992; Z. Cymerman, 1992b; H. Fossen, B. Tikoff, 1993; R.

W. Krantz, 1995). It simply means that fold axis cannot be used to determine the X, Y, and Z axes of the finite strain ellipsoid. Scattered attitude of folds and lineation as well as

"superimposed" fold structures, frequently non-cylindrical and with curvilinear course of fold crest (e-g. S. Cwojdziriski, 1982) were customarily interpreted as the result of several independent deformation stages (e.g. S. CwojdziAski, 1975,1976~1,1977,1979; I. Wojcie chowska, 1975,1993; M. Dumicz, 1989). Lately, J. ~ a b a and Bgdkowski (1995) presented a sequence of up to seven consecutive generations of shear zones (SzS7) in the Zloty Stok area.

CurrentIy, a common idea is accepted that fold axes with orientation almost parallel to direction of tension X of the finite strain ellipsoid have formed as the result of progressive rotation from their initial orientation being close to intermediate axis Y of the finite strain ellipsoid (A. Escher, J. Watterson, 1974; P. R. Cobbold, H. Quinquis, 1980; J. Ridley, 1986). This requires strong deformations of simple shear type (with y

>

⁼ 10 for example) and passive fold development up to formation of structures of sheath fold type (P. R.

Cobbold, H. Quinquis, 1980). However, a lot of natural folds with their axes p d e l to extensional lineation Lx do not exhibit features of sheath folds, and kquently they are structures of open type without clear evidences of very strong strains supposed to be

, connected with their development. Their development is connected with active (dyna&c) folding of rock media showitig distinct differences in rheological properties.

If folds are younger than the extensional lineation Lx, then shear factors on their limbs are characterized by opposite shear senses. Such relationship is missing in the Bzowiec fold being a largest fold structure within the area under present study. Observations exclude the possibility of rotation and deflection of limbs of the Bzowiec fold after the shear type